Constraints on Effective Field Theory for Dark Energy

Positivity Bounds on Dark Energy: When Matter Matters

Positivity bounds-constraints on any low-energy effective field theory imposed by the fundamental axioms of unitarity, causality and locality in the unitary ultraviolet-have recently been used to constrain scalar-tensor theories of dark energy.We show that demanding positivity when including interactions with standard matter fields leads to further constraints on the dark energy parameter space and explicitly illustrate the impact on a specific effective field theory for dark energy.We also show in this model that the existence of a standard ultraviolet completion requires that gravitational waves must travel superluminally on cosmological backgrounds.